1. Field of the Invention
The present invention relates to a thermal head, a cleaning method thereof that may remove organic substances adhered to the surface of the thermal head by photolyzation, and a color thermal printer.
2. Description Related to the Prior Art
As a thermal printer, the well-known type is a color thermal printer coloring and recording a full-color image by heating a color thermal recording sheet by means of the thermal head. The color thermal recording sheet is composed of a cyan thermal coloring layer on top of the base, a magenta thermal coloring layer, a yellow thermal coloring layer and a transparent protective layer laminated in the order mentioned. The yellow thermal coloring layer, the magenta thermal coloring layer, and the cyan thermal coloring layer are thermically recorded in the order mentioned when the color thermal recording sheet is pressed against the thermal head, to which a predetermined amount of thermal energy is sent. The transparent protective layer is provided for protecting the thermal coloring layers and improving the quality of print image by lustering the surface of the recording sheet. The transparent protective layer is composed of denatured-silica polyvinylalcohol (silica modified polyvinyl alcohol), silicon based lubricant, acetylene glycol, zinc stearate, and the like.
Since the thermal head is pressed against the color thermal recording sheet as recording image, the transparent protective layer is softened by heat, and its organic substances adhere on the surface of the thermal head as stains. Cleaning of the surface of the thermal head is required, as the stains deteriorate the quality of print image by hindering heat transfer. In U.S. Pat. No. 6,271,872, for example, a cleaning is executed by grinding the thermal head to remove the stains thereon by means of a cleaning sheet fed between the thermal head and a platen roller.
The conventional cleaning method, however, is to grind the surface of the heating elements with the use of cleaning sheet having a grind layer, and that causes a problem that the surface of the thermal head is abraded by being grinded, which deteriorates the quality of print image.
The present invention is invented in consideration of the problem described above, and an object of the present invention is to provide a thermal head and a cleaning method thereof that may clean the thermal head without touching it.
In order to achieve the above-described object, the thermal head of the present invention is characterized in being provided with a photocatalytic layer on the surface of the heating element array.
In a preferred embodiment, the thermal head is disposed in a color thermal printer that has a fixation lamp to generate fixation light for optical fixation of an image recorded on a recording sheet. The fixation light from the fixation lamp is reflected on a recording sheet guide toward the photocatalytic layer when the platen roller is shifted to be away from the heating element array. It is possible to guide the fixation light by rotating a part of a reflection plate to cover the fixation lamp. The fixation lamp and the heating element array may be swung to face each other so that fixation light is directly applied to the photocatalytic layer.
Since the photocatalytic layer photolyzes and removes the substances on the thermal head by applying ultraviolet light, it is possible to clean the thermal head without causing abrasion of the thermal head. Moreover, no exclusive lamp is required since the ultraviolet light is applied to the photocatalytic layer by the fixation lamp to fix the recorded image. Furthermore, since the fixation light is guided toward the photocatalytic layer, it is possible to apply the fixation light efficiently.